The need for psychiatrists in the military was recognized for the first time during World War I, which involved millions of men in unusually protracted warfare. The policy of treating psychiatric casualties close to the from and returning soldiers to their military units as quickly as possible proved of great significance in the U.S. war effort. During World War II, the Korean conflict, and the war in Viet Nam, military psychiatry made great contributions and learned many lessions, both at home and abroad. The lessions learned by military psychiatry have important applications for the rest of medicine, especially in the fields of stress, crisis therapy, and community psychiatry.